The invention relates to the field of integrated optics and more particularly to the application of integrated optics to voltage-sensing devices.
Integrated optics is the term used to describe a class of optical devices made using techniques borrowed from the field of integrated electronics. Mono-mode optical waveguides, with extremely small cross-sections, can be made by numerous techniques including diffusion into and thin film deposition onto crystal substrates. Signals can then be transmitted to and from these devices on optical fibres.
The application of integrated optics to temperature sensors is disclosed in a paper of L. M. Johnson, F. J. Leonberger and G. W. Pratt entitled "Integrated Optical Temperature Sensor", Appl, Phys. Lett 41 (2), July 15, 1982. The article discloses the use of a waveguide version of the Mach-Zehnder interferometer in which the input optical waveguide splits into two arms of unequal lengths which then recombine to form an output waveguide. The difference in path length between the two arms is substantially greater than the optical wavelength of the transmitted light. The optical transmission at a given wavelength varies with the effective index of refraction of the arms and path length difference, both of which are in turn temperature-dependent. Hence, changes in the temperature of the device can be detected through variations in the optical transmission.
The application of optical devices to use as high voltage sensors, for example in power transmission lines and substations, is also known. Such devices have been based on the Pockel's and Kerr effects in electro-optic materials. The advantages of optical systems in such applications over conventional voltage transformers are electrical isolation, immunity to electrical noise, the application to potentially large band widths, low cost and small size. Existing sensors, however, are complicated optical sytems employing lenses, polarizers, beam splitters, optical fibre couplers and bulk electro-optic crystals. Such systems are bulkier and more expensive than would be an integrated optical system. Also, the use of large crystals in such bulk devices results in ringing or oscillation which occurs due to the converse piezo-electric and photo-elastic effects.